Arc lamp having acceleration actuated ignition means



Sept. 8, 1970 A. H. SCHWARTZ 3,527,983

ARC LAMP HAVING ACCELERATION ACTUATED IGNITION MEANS Filed June 10, 1968 INVENTOR.

ALF'RED H. SCHWARTZ ATTQRNEYS United States Patent 3,527,983 ARC LAMP HAVING ACCELERATION ACTUATED IGNITION MEANS Alfred H. Schwartz, San Mateo, Calif., assignor to Varian Associates, Palo Alto, Calif, a corporation of California Filed June 10, 1968, Ser. No. 735,833 Int. Cl. H013 7/38; H01i 61/54 US. Cl. 315357 13 Claims ABSTRACT OF THE DISCLOSURE An arc lamp having acceleration actuated ignition means. The lamp comprises two electrodes mounted in ionizable gas confined within a lamp housing. Means are disclosed for moving one electrode relative to the other upon acceleration of the housing and for arresting this relative motion. This structure permits the lamp to be ignited by positioning the electrodes in abutment, applying electric power to the electrodes, and accelerating the lamp housing thereby causing the electrodes to separate and acquire a potential difference which ionizes gas therebetween.

BACKGROUND OF THE INVENTION This invention relates to novel means for igniting arc lamps.

High intensity are lamps comprise two electrodes, connectable to a source of electric power, which are spaced apart to define an arc gap therebetween. Once the lamp is ignited gas within the arc gap is ionized providing a relative low resistive path for electron flow between the electrodes. This electron flow produces radiation in the ultraviolet, visible and/or infrared region of the spectrum, depending on the chemical composition of the gas and the electrodes. As the arc has relatively low resistance, only a modest potential difierence is required between the electrodes to maintain the lamp in an operative mode. Before lamp ignition, however, the gas in the arc gap is not ionized. In such a state there exists relatively few electrons which are free of their atomic orbital confines which are available to flow across the arc gap. As a result the are lamp has high electrical resistance prior to ignition.

To break down and ionize the gas in igniting the lamp either the gap resistance must be temporarily reduced or a voltage impressed thereacross greatly in excess of that required for sustained operation. Heretofore several means have been used in achieving this. In the arc lamps typically used in comercial motion picture projectors, for example, consumable carbon electrodes are brought together manually by mechanical linkage. In doing this the resistance between the electrodes is temporarily reduced to such a degree that the normal operating voltage itself is sufiicient to ionize gas at the interface of the electrodes. Following ignition the two electrodes are manually separated to their operating positions during which transient period ambient gas entering the expanding gap ionizes in avalanche fashion. In other special cases electromagnetic means are used in bringing together and separating the electrodes.

High intensity are lamps also exist having electrodes confined in a pressurized gaseous medium other than air. Inert gases such as xenon, argon, and krypton, and metal vapors such as mercury, cesium, rubidium, sodium, potassium and lithium are most commonly used, the selection of gas being dependent on spectral requirements. These lamps usually have their electrodes sealed in a transparent are tube or bulb which normally is made of quartz. As

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the electrodes are sealed, they cannot be brought into contact for ignition purposes. In such cases a high voltage in the order of several kilovolts is impressed across the arc gap which ionizes the gas in igniting the lamp. The voltage is then reduced to an operational level such as 10 to 30 volts. Such an ignition system has several inherent problems. First it requires a source of very high voltage. For one-shot applications, such as may be used in optical tracking elements of airborne vehicles, the ignition power supply with its attendant weight, must be carried by the airborne vehicle for but a single instance of use. Additionally, the power supply must be electrically interconnected with the operating power supply in such a manner that neither the operating power supply nor the arc lamp itself will be burned out by the ignition power surge. Furthermore, this surge of power may cause a temporary but strong disintegration of the electrodes themselves which deposits on the transparent bulb thereby reducing the radiation efiiciency of the lamp.

Several approaches have heretofore been taken in mitigating the enumerated problems associated with fixed positioned, high voltage ignited arc lamps. In US. Pat. 3,303,377, for example, a thoriated tungsten Wire is used in conjunction with axially aligned spaced conical tungsten electrodes. As thorium oxide readily emits electrons, the required voltage for ignition is reduced. The emissive wire is so located as not to emit electrons itself following ignition for are stabilization purposes. In U.S. Pat. 3,343,033 an alternative path is provided between the electrodes which has low resistance to the high frequency electric energy used for lamp ignition, but high resistance to the relatively low frequency of the operating energy. In US. Pat. 3,363,132 a third, starting electrode is introduced into the arc tube in close proximity to one of the operating electrode. This operating electrode has an extension arm which bridges a substantial portion of the space between the starting electrode and the proximate, operating electrode. The short starting gap provides reduced ignition resistance which lowers the required ignition voltage. In US. Pat. 3,377,497 the arc gap is completely traversed by a consumable bridge-wire greatly reducing the gap resistance and ignition voltage.

Each of the above approaches has its advantage; each however also has its disadvantages. The starting wire of the first cited reference is located at a distance from the anode requiring higher voltage for ignition than that required for sustained operation. The second reference teaches a relatively complex and thus expensive structure. The third reference, besides being a long arc lamp, introduces a third electrode with its additional circuitry and requires a source of RF energy for ignition. The bridge wire of the last reference vaporizes and contaminates the arc tube atmosphere and its transparent window.

Accordingly, it is an object of the present invention to provide an arc lamp having improved ignition means.

More particularly, it is an object of the invention to provide novel means for igniting an arc lamp using only the relatively low voltage source required for sustained lamp operation. In achieving this object the need for relatively heavy, high voltage insulators is simultaneously eliminated.

Another object of the invention is to provide means for igniting an arc lamp without the introduction of a third electrode or appendage to the operating electrodes.

Yet another object of the present invention is to provide a high intensity are lamp uniquely suited for use in a vehicle or other machine which is subjected to aceleration.

Yet another object of the invention is to provide an arc lamp having resettable ignition means.

3 Another object of the invention is to provide an arc lamp which may be ignited, operated and extinguished with safety even when manually operated under water.

SUMMARY OF THE INVENTION Briefly described the present invention is an arc lamp having acceleration actuated ignition means. The lamp comprises a housing which confines an ionizable gas and two electrodes mounted therewithin. Means are provided for producing a relative movement between the electrodes upon acceleration of the lamp housing and for arresting this relative movement at predetermined relative positions of the electrodes. With this structure the arc lamp may be ignited by positioning the electrodes in abutment, applying electric power thereto, and accelerating the lamp housing thereby causing the electrodes to separate and acquire a potential difference which ionizes gas therebetween.

In one embodiment an electrode is mounted in a dashpot. In another embodiment an electrode is mounted on a bi-stable support structure.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1A is an elevational view in cross-section of a high intensity short are lamp having one embodiment of the acceleration actuated ignition means of the present invention. FIG. 1B is a frontal view of the lamp in FIG. 1A.

FIG. 2A is a cross-sectional view of the high intensity are lamp of FIG. 1 having another embodiment of the ignition means of the present invention. FIG. 2B is a frontal view of the lamp shown in FIG. 2A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now in more detail to the drawing, there is illustrated in FIGS. 1A and 1B a high intensity short are lamp having a ceramic, tubular member brazed to a copper ring 12 which in turn is brazed to a Kovar or stainless steel ellipsoidal member 14. Each of these members forms a portion of the lamp envelope, the inner surface of member 14 also serving as integral reflector 16. The other end of ceramic member 10 is brazed to a copper ring 18 which in turn is brazed to one side of a Kovar terminal ring 20. The terminal ring is then brazed to another copper ring 22 which in turn is brazed to the flange of a tubular, Kovar window support 24. The Periphery of a disc-shaped sapphire window 26 is slightly recessed within and brazed to window support 24.

A rod-shaped tungsten anode 30 is press-fitted into dashpot 32 which is supported along the axis of tubular ceramic member 10 and sapphire window 26 by three triangular, molybdenum supports 34. Each support has a notch into which terminal ring is brazed. Supports 34 provide electrically conductive paths between anode and terminal ring 20.

The top of a rod-shaped thoriated tungsten cathode 38 is coaxially supported in abutment with the tip of anode 30 by Kovar cup 40. This cup, which forms a portion of the sealed envelope, is brazed about the periphery of an aperture in ellipsoidal member 14. A copper exhaust tubulation 42 communicates through the cup into the interior region of the lamp envelope. Once the envelope has been filled with gas and pressurized, the copper tubulation is pinched off thereby confining the pressurized gas within the sealed envelope.

When electric power is supplied to anode 30 and cathode 38 they act as ordinary conductors since they are in abutment. However, when the lamp is accelerated from right to left the inertia of anode 30 causes it to slide within dashpot 32. In so sliding gas is forced out of the dashpot through vent 36 in the rear wall thereof. This vent is dimensioned to restrict the flow of exiting gas in controlling the velocity of sliding anode 30 with respect to the dashpot. In this manner the impact of the anode on the rear wall of the dashpot is cushioned. The dashpot bore may also be reduced from front to rear in further dampening this impact.

Once anode 30 has contacted the rear wall of dashpot 32 its tip assumes the position indicated in broken lines. The spacing between the newly positioned anode and cathode corresponds to the travel of the anode within the dashpot and defines the operating arc gap of the lamp. When the anode commenced its travel away from cathode 38 the initial gap therebetween was of course very slight. At that point the operating voltage applied to the electrodes was in itself suflicient to ionize the gas therebetween. As the arc gap expanded the additional gapoccupying gas also ionized in avalanche fashion. Once the operating gap was established and lamp acceleration terminated, the press-fit between the anode and dashpot prevents further alteration in arc gap size through further anode movement.

FIGS. 2A and 2B illustrate another embodiment of the invention. A ceramic, tubular member is brazed to a copper ring '52 which in turn is brazed to a Kovar or stainless steel ellipsoidal member 54 having an inner surface 56 which serves as an integral reflector. The other end of the ceramic member is brazed to a copper ring 58 which in turn is brazed to one side of a terminal ring 60. The terminal ring is then brazed to another copper ring 62 which in turn is brazed to the flange of a tubular, Kovar window support 64. The periphery of a discshaped sapphire window 66 is slightly recessed within and brazed to the window support.

A rod-shaped tungsten anode 70 is supported by three struts 72 which are brazed about anode prong 74. Struts 72 extend radially from the anode to terminal ring into which they merge forming an integral structure. The struts and terminal ring are preferably made of a molybdenum-nickel alloy such as Hastelloy X.

The tip of a rod-shaped thoriated tungsten cathode 76 is co-axially supported in abutment with the tip of anode by Kovar cup 80. A copper exhaust tubulation 82 communicates through the cup into the interior region of the lamp envelope. Once the envelope has been filled with gas and pressurized, the copper tubulation is pinched off thereby confining the pressurized gas within the sealed envelope.

FIG. 2A illustrates with solid lines the tip of anode 70 in contact with the tip of cathode 76. In this position struts 72 are shown in solid lines as being slightly flexed to the left of vertical. This is one of two stable positions which elastically bi-stable struts 72 may take when mounted within the lamp envelope. The other stable position which the struts may take is shown in broken lines as flexed to the right of vertical. Anode 70 is shown also in broken lines in their latter position.

When electric power is supplied to anode 70 and cathode 76 they act as ordinary conductors since they are pressed together in abutment. However, when the lamp is accelerated from right to left the inertia of anode 7t) and struts 72 cause them to move to the right relative to the lamp envelope, away from cathode 76 to their position shown in broken lines. This repositioning of the two electrodes causes the lamp to ignite as explained in the discussion of the embodiment shown in FIGS. 1A and 1B. The embodiment shown in FIGS. 2A and 2B however has the additional capability of acceleration actuated arc extinction: Should the lamp be accelerated from left to right the inertia of anode 70 and struts 72 will cause them to move to the left and re-contact cathode 76.

Obviously many modifications may be made in the two illustrated examples without departing from the spirit and scope of the invention as set forth in the concluding claims. For example, either the cathode, the anode or both may be selected for moveable mounting. Furthermore, either the electrode located adjacent the lamp window or remote therefrom may be the one moveably mounted depending on whether ignition is to occur upon positive or negative acceleration of the lamp. Also many materials may be substituted for those employed in the preferred embodiments. If required a set of rigid struts may be mounted in the shadow of the 'bi-stable struts to provide reinforced arrestment means.

What is claimed is:

1. An arc lamp comprising a housing confining an ionizable gas, two electrodes mounted within said housing adjacent one another, means for producing relative movement between said electrodes upon acceleration of said housing, means for arresting said relative movement at first and second predetermined relative positions of the electrodes, and means for maintaining said electrodes in either said first or second position, said electrodes being in abutment in said first position and being spaced apart a selected fixed distance in said second position to define an arc gap there'between whereby the arc lamp may be ignited by positioning the electrodes in abutment, applying electric power to the electrodes, and imparting a first acceleration to the lamp housing thereby causing the electrodes to assume said second position and acquire a potential difference which ionizes gas therebetween.

2. An arc lamp in accordance with claim 1 wherein one of said electrodes is rigidly mounted in said housing.

3. An arc lamp in accordance with claim 1 wherein said electrodes are cylindrical and coaxially mounted.

4. An arc lamp in accordance with claim 3 wherein one of said electrodes is mounted for axial movement.

5. An arc lamp in accordance with claim 3 wherein said housing comprises an optical window disposed transverse to the axis of said electrodes.

6. An arc lamp in accordance with claim 1 wherein said means for producing relative movement between said electrodes includes a dashpot in which a portion of one of said electrodes is positioned to slide upon acceleration of the lamp housing.

7. An arc lamp in accordance with claim 6 wherein said portion of said one electrode is press-fitted into said dashpot.

8. An arc lamp in accordance with claim 6 wherein said means for arresting said relative movement includes said dashpot.

9. An arc lamp in accordance with claim 1 wherein said means for producing relative movement between the electrodes includes an elastically bi-stable support structure.

it An are lamp in accordance with claim 9 wherein said means for arresting said relative movement includes said elastically bi'stable support structure.

11. An arc lamp in accordance with claim 9 wherein said elastically bi-stable support structure comprises at least two struts compressively aflixed to one of said electrodes and to said housing when oriented normally thereto.

12. An arc lamp in accordance with claim 11 having an externally accessible electrical terminal and wherein at least one of said struts provides an electrically conductive path between said electrode and said terminal.

13. An arc lamp according to claim 1 wherein said means for maintaining permits return of said electrodes to said first position only in response to a second acceleration of said housing having a component in a direction opposite said first acceleration, said component having a magnitude exceeding a preselected level.

References Cited UNITED STATES PATENTS 2,156,369 5/1939 Bay 313-184 X 2,566,704 9/1951 Leibing 3l3148 X 2,839,701 6/1958 Bourns 313146 3,418,507 12/1968 Young 313184 X JAMES W. LAWRENCE, Primary Examiner P. C. DEMEO, Assistant Examiner U.S. Cl. X.R. 313-446, 184 

